U.S. patent number 9,518,561 [Application Number 13/642,112] was granted by the patent office on 2016-12-13 for method for the operation of a wind turbine.
This patent grant is currently assigned to Wobben Properties GMBH. The grantee listed for this patent is Alfred Beekmann, Wolfgang De Boer, Georg Eden, Gerhard Lenschow. Invention is credited to Alfred Beekmann, Wolfgang De Boer, Georg Eden, Gerhard Lenschow.
United States Patent |
9,518,561 |
De Boer , et al. |
December 13, 2016 |
Method for the operation of a wind turbine
Abstract
The invention relates to a method for operating a wind turbine
comprising an aerodynamic rotor that has at least one rotor blade.
Said method comprises the steps of operating the wind turbine at an
operating point that depends on the wind speed, detecting an
operating parameter of the operating point, comparing the detected
operating parameter with a predetermined reference quantity, and
heating the at least one rotor blade when the detected operating
parameter exceeds a predetermined variation from the reference
quantity, the operation of the wind turbine being continued.
Inventors: |
De Boer; Wolfgang (Moormerland,
DE), Eden; Georg (Westerholt, DE),
Beekmann; Alfred (Wiesmoor, DE), Lenschow;
Gerhard (Aurich, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
De Boer; Wolfgang
Eden; Georg
Beekmann; Alfred
Lenschow; Gerhard |
Moormerland
Westerholt
Wiesmoor
Aurich |
N/A
N/A
N/A
N/A |
DE
DE
DE
DE |
|
|
Assignee: |
Wobben Properties GMBH (Aurich,
DE)
|
Family
ID: |
44834557 |
Appl.
No.: |
13/642,112 |
Filed: |
April 12, 2011 |
PCT
Filed: |
April 12, 2011 |
PCT No.: |
PCT/EP2011/055737 |
371(c)(1),(2),(4) Date: |
January 02, 2013 |
PCT
Pub. No.: |
WO2011/131522 |
PCT
Pub. Date: |
October 27, 2011 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20130106108 A1 |
May 2, 2013 |
|
Foreign Application Priority Data
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|
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Apr 19, 2010 [DE] |
|
|
10 2010 015 595 |
Apr 8, 2011 [DE] |
|
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10 2011 007 085 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03D
1/0675 (20130101); F03D 7/048 (20130101); F03D
80/40 (20160501); F03D 7/0264 (20130101); F03D
7/045 (20130101); F03D 80/60 (20160501); F05B
2260/20 (20130101); F05B 2270/325 (20130101); Y02E
10/72 (20130101); F05B 2270/335 (20130101); F05B
2270/32 (20130101) |
Current International
Class: |
F03D
7/02 (20060101); F03D 7/04 (20060101); F03D
1/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO |
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WO |
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Dec 2012 |
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WO |
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Other References
Sarkar, Asis et al., "Wind Turbine Efficiency and Power Calculation
with Electrical Analogy", Feb. 2, 2012, International Journal of
Scientific and Research Publications, vol. 2, Issue 2. cited by
examiner.
|
Primary Examiner: Keasel; Eric
Assistant Examiner: Corday; Cameron
Attorney, Agent or Firm: Seed Intellectual Property Law
Group LLP
Claims
The invention claimed is:
1. A method of operating a wind power installation having an
aerodynamic rotor with at least one rotor blade, the method
comprising: operating the wind power installation at an operating
point dependent on the wind speed; detecting an operating parameter
of the operating point, wherein the detected operating parameter is
electric power being generated by the wind power installation;
comparing the detected operating parameter to a first tolerance
range and a second tolerance range of a reference parameter, the
first tolerance range being within the second tolerance range;
heating the at least one rotor blade in response to the detected
operating parameter being outside of the first tolerance range and
within the second tolerance range, while continuing the operation
of the wind power installation; and stopping or shutting down the
wind power installation in response to the detected operating
parameter being outside of the first tolerance range and the second
tolerance range.
2. The method according to claim 1, wherein the wind power
installation is at least one of stopped and powered down, the
method further comprising: restarting the wind power installation;
detecting the operating parameter of the operating point for a
period of time; comparing the detected operating parameter for the
period of time to the second tolerance range; and at least one of
stopping and powering down the wind power installation when the
detected operating parameter for the period of time is outside of
the second tolerance range over the period of time.
3. The method according to claim 1, further comprising detecting
wind speed proximate the wind power installation, wherein the
reference parameter depends on the detected wind speed.
4. The method according to claim 1 wherein heating the at least one
rotor blade comprises blowing heated air through the rotor
blade.
5. The method according to claim 4 wherein blowing heated air
through the rotor blade comprises blowing heated air through a
conduit in the rotor blade.
6. The method according to claim 1, further comprising: detecting a
temperature at or proximate the wind power installation; and at
least one of stopping and powering down the wind power installation
when the detected temperature exceeds a threshold minimum
temperature and when the detected operating parameter exceeds a
threshold deviation relative to the reference parameter.
7. The method according to claim 1 wherein heating the at least one
rotor blade comprises heating the at least one rotor blade when the
detected operating parameter exceeds a threshold deviation for a
threshold amount of time.
8. A wind power installation comprising: a rotor having at least
one rotor blade that includes a main portion and an end portion,
wherein the main portion includes an air guide conduit configured
to deliver heated air through the main portion to an interior of
the end portion; a heating device; a blower; and a control unit
configured to detect electric power generated by the wind power
installation and to compare the detected electric power to first
and second threshold reference parameters, the control unit
configured to, in a first operation, activate the heating device
and the blower in response to the detected electric power exceeding
a deviation of the first threshold reference parameter and to cause
heated air to blow through the air guide conduit of the main
portion of the at least one rotor blade while the wind power
installation is in operation, the control unit configured to, in a
second operation, power down the wind power installation in
response to the detected electric power exceeding a deviation of
the second threshold reference parameter.
9. The wind power installation according to claim 8 further
comprising an anemometer configured to measure wind speed proximate
the rotor, wherein the first and second threshold reference
parameters are dependent on wind speed.
10. The wind power installation of claim 8 wherein the control unit
is configured to activate the heating device and the blower in
response to the detected electric power exceeding the deviation of
the threshold reference parameter for a threshold period of
time.
11. A method of operating a wind power installation comprising an
aerodynamic rotor having at least one rotor blade, the method
comprising: monitoring whether there is icing on the wind power
installation by measuring the electric power generated by the wind
power installation; and when the electric power passes a first
threshold, heating the at least one rotor blade, while operation of
the wind power installation is continued, and when the electric
power passes a second threshold that is less than the first
threshold, powering down the wind power installation.
12. A method of operating a wind park comprising a plurality of
mutually communicating wind power installations, each of the wind
power installations comprising an aerodynamic rotor having at least
one rotor blade, the method comprising: monitoring whether there is
icing on at least one of the wind power installations by measuring
the electric power generated by the at least one of the wind power
installations; and when the electric power passes a first
threshold, heating the at least one rotor blade of each of the wind
power installations in the wind park, while operation of each of
the wind power installations of the wind park is continued, and
when the electric power passes a second threshold that is less than
the first threshold, powering down the wind power installation.
Description
BACKGROUND
Technical Field
The present invention concerns a method of operating a wind turbine
or wind power installation and a corresponding wind power
installation.
Description of the Related Art
Methods of operating a wind power installation have long been
known. Thus it is for example usual for wind power installations to
be operated on the basis of a predetermined power characteristic
which depends on the wind speed. In the case of wind power
installations with rotor blades involving an adjustable rotor blade
angle--generally also referred to as the pitch angle--that can also
be adjusted to implement the respectively desired operating point
of the wind power installation.
Such methods of operating a wind power installation however can
encounter their limits if unforeseen or unusual circumstances occur
such as for example icing on parts of the wind power installation.
A particular problem in that respect is represented by icing of the
rotor blades. Such icing causes problems because it can result in
ice dropping off the rotor blades, which is dangerous for people
who are below the rotor blades. The danger of such dropping ice can
be increased if the wind power installation should continue to be
operated in that condition.
Another problem with icing on the rotor blades is that the
properties of the wind power installation are altered and
regulation of the installation can be disturbed thereby. In
addition, depending on the respective amount of ice formation on
the wind power installation, in particular on the rotor blades,
there is the risk of damage to the wind power installation.
Methods are known which try to detect ice formation on the rotor
blades in order then to stop the wind power installation and shut
it down to protect it. In addition, the attempt can be made to
remove the ice, in the stopped condition of the installation. DE
103 23 785 A1 describes a method of detecting ice accretion.
A problem in that respect is that of reliably detecting ice
accretion. Because safety aspects involve a high and usually the
highest priority, shut-down of the installation is often already
effected when there is a suspicion of ice accretion. That can
result in unwanted and, considered objectively, unnecessary wind
power installation stoppage times. Depending on the respective
erection site that can add up to considerable economic losses.
BRIEF SUMMARY
The object of the present invention is as far as possible to
eliminate or to reduce the aforementioned disadvantages. In
particular the invention seeks to propose a solution which
increases the efficiency of a wind power installation, and in
particular provides an improvement in the operating characteristics
of a wind power installation upon ice accretion or with the threat
of ice accretion. At least the invention seeks to propose an
alternative solution.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 diagrammatically shows a power-optimized characteristic with
a first and a second tolerance range for the power of a wind power
installation in dependence on the wind speed,
FIG. 2 diagrammatically shows power characteristics similarly to
FIG. 1, but for a sound-optimized mode of operation,
FIG. 3 diagrammatically shows a partly sectional view of a rotor
blade with indicated circulating air flow,
FIG. 4 shows a partly sectional perspective view of a rotor blade
according to a further embodiment, and
FIG. 5 shows another view of a portion of the rotor blade of FIG.
4.
The Figures hereinafter can have identical references or
identifications for similar but possibly not identical
features.
DETAILED DESCRIPTION
A method according to one embodiment of the invention of operating
a wind power installation is based in particular on a wind power
installation comprising a foundation carrying a pylori, at the
upper end of which is arranged a pod. The pod has at least one
generator and an aerodynamic rotor connected directly or indirectly
thereto. In particular the arrangement adopted as the basic
starting point has a rotor with a substantially horizontal axis and
a hub with at least one and preferably three rotor blades.
The wind power installation is operated at an operating point
dependent on the wind speed. For example, based on a predetermined
rotary speed-dependant power characteristic, the electrical power
delivered by the generator is adjusted until a steady-state
operating point with a predetermined rotary speed and a given
delivered power is set. That operating point is dependent on the
wind speed. At least one operating parameter of that operating
point is detected. For example the electrical power delivered by
the generator is detected and forms the detected operating
parameter. That can be a measurement value or a value calculated
from one or more measurement values. The detected operating
parameter used can also be an internal calculated parameter or
control parameter which is afforded for example upon operation of
the wind power installation at the operating point or is detected
in any case.
The detected operating parameter--in the foregoing example the
delivered electrical generator power--is compared to a
predetermined reference parameter. In accordance with the above
example, this involves a comparison of the detected power with a
reference power.
If now the detected operating parameter exceeds a predetermined
deviation in relation to the detected reference parameter, at least
one rotor blade is heated, in which case operation of the wind
power installation is continued. Preferably in that case all rotor
blades of the wind power installation are heated. The reference to
continuation of operation of the wind power installation is used
here in particular to mean that the rotor continues to rotate and
the generator continues to deliver electrical power which continues
to be fed into an electric network, such as an electric three-phase
ac voltage network.
Heating can be made dependent on further boundary conditions.
The reference parameter used is in particular a value typical of
the present operating point, in particular the wind speed
prevailing in this case. The detected value which can also be
referred to as the actual value is thus compared to a value
expected under normal conditions. Minor deviations are permitted.
If however a predetermined deviation relative to the reference
parameter is exceeded, that is assumed to be an atypical operating
condition. It was now realized that it may be advantageous, in the
event of a deviation which points to ice accretion at a rotor
blade, not to stop and shut down the wind power installation but to
continue to operate it and to counteract the assumed icing by
heating of the rotor blade. The predetermined deviation between the
detected operating parameter and the corresponding reference
parameter can in that case be so selected that ice accretion is
counteracted at an early stage. Stopping and shutting down the
installation can thus be prevented at times. By virtue of the
option afforded in that way, of continuing to operate the wind
power installation in spite of the suspicion of ice accretion, the
wind power installation can continue to be operated and thus
efficiency can be increased in situations, particularly in winter,
when hitherto the wind power installation would have had to be shut
down. Particularly in winter that provides that the amount of
electrical energy delivered by the generator can be increased. The
method can also be preventatively used by virtue of early detection
of ice accretion and implementation of heating of the rotor
blades.
The predetermined deviation can be provided as a fixed value by
which the detected operating parameter is not to rise above or fall
below the reference parameter. It may however also be considered
that the deviation is selected differently in respect of exceeding
the predetermined reference parameter on the one hand and falling
below the predetermined reference parameter on the other hand. The
predetermined deviation can also be selected to be different
depending on the respective operating point or in dependence on
other parameters.
Preferably a first tolerance range and a second tolerance range are
predetermined in relation to the reference parameter in question,
the first tolerance range being within the second tolerance range.
The respective reference parameter is disposed in both tolerance
ranges. The two tolerance ranges however do not have to uniformly
include the reference parameter. Rather, a limit of the first
tolerance range can also coincide with the limit in question of the
second tolerance range and at the same time the other limit of the
first tolerance range can define a smaller spacing relative to the
reference parameter than the corresponding limit of the second
tolerance range.
The underlying idea here is that optimum power conversion of the
prevailing wind into electrical power to be delivered by the
generator is achieved with rotor blades without ice accretion. If
now--for the example of detection of the delivered power of the
generator as the detected operating parameter--slight deviations
occur between the detected power and the reference power, it is
firstly assumed that natural fluctuations or alterations in some
boundary parameters such as air density are the underlying cause
here. The wind power installation can thus continue to be operated
without change, for such slight deviations.
If however the detected operating parameter is outside the first
tolerance range and thus exceeds a first predetermined deviation,
it is to be assumed that this involves an unusual situation such as
for example ice accretion. If in that case the detected operating
parameter is still within the second tolerance range, it is assumed
that this involves ice accretion which is not yet so severe. In
that case the wind power installation does not need to be stopped
or shut down, but heating of the rotor blade is effected to
counteract the ice accretion.
If now the deviation is so great that the detected operating
parameter is also outside the second tolerance range then it is
assumed that this situation involves an excessively great ice
accretion so that the wind power installation is stopped. On the
other hand this situation can also include a fault, for example in
detection of the operating parameter. In this case also the
installation is to be stopped.
If the detected power is above the reference power, that is to say
above the usual power, it is to be assumed that this does not
involve ice accretion but rather a measurement disturbance or
another fault or disturbance. In that case the limit value of the
first tolerance range and the second tolerance range is the same
value because heating of the rotor blade in the case of a
measurement fault is not desirable. If however the detected power
is below the reference power and thus below the expected value,
that indicates a worsening of efficiency of the wind power
installation, which points to ice accretion. In that case therefore
heating of the rotor blade is effected to counteract the icing
insofar as the deviation is not yet so great.
If however the deviation is too great, namely so great that the
detected operating parameter is outside the second tolerance range,
then the wind power installation is stopped and/or shut down to
obviate any damage. An excessive deviation can also point to a wind
power installation control system which is not operating
correctly.
In a further embodiment it is proposed that the detected operating
parameter is the power, in particular the power produced by the
wind power installation, that is to say by the generator, and/or
the current wind speed is detected and the reference parameter is
dependent on the wind speed. In particular the reference parameter
is stored as a reference characteristic dependent on the wind
speed. A possible way of recording such a reference characteristic
is described in DE 103 23 785 A1.
To compare the detected operating parameter to the reference value
the procedure involved can be as follows. For the wind power
installation, an operating point is set in dependence on a
predetermined relationship between rotary speed and power. In
addition the prevailing wind speed is measured, wherein that
measurement value was not used for setting the operating point. In
relation to that measured wind speed value, a reference value for
the power, which is set usually under normal conditions, is stored
in a characteristic curve or a reference table--a so-called lookup
table --. The detected power which has been produced when setting
the operating point is compared to that value of the power, that is
stored in relation to the currently prevailing wind speed.
If, with the currently prevailing operating point, the situation
involves normal boundary conditions, in particular no icing, a
power which approximately corresponds to the power stored in
relation to the currently prevailing wind speed, as the reference
parameter, may be set when setting the operating point. Slight
deviations can be tolerated. If greater deviations occur it can be
assumed that the situation involves slight icing and heating of the
rotor blade is caused to occur. In particular that happens when the
detected power is less than the associated reference value.
When the deviation is above a particular level, stoppage and/or
shut down of the installation should be effected.
The use of the power is only one possibility which is proposed in
particular in relation to wind power installations with an
adjustable rotor blade angle in the so-called part-load range. In
the part-load range, the rotor blade angle is usually not adjusted
but rather is constant over the entire part-load range, that is to
say for wind speeds from a start-up wind speed at which the wind
power installation first starts at all, to a nominal wind speed at
which the wind power installation has reached its nominal rotary
speed and nominal power, under normal conditions.
In that full-load range, basically regulation of the rotary speed
is effected by adjusting the rotor blade angle--so-called pitch
adjustment--to the nominal rotary speed. The power is regulated to
the nominal power. Thus--at any event in the ideal case--the power
and the rotary speed are constant in the full-load mode of
operation. Thus there also cannot be any wind speed-dependent
deviation in the set power, from the reference power. The set power
is here unsuitable as an indicator for icing.
In a corresponding fashion, in the full-load mode of operation a
comparison of the set rotor blade angle to a reference rotor blade
angle is proposed. The reference rotor blade angle is also stored
in dependence on the wind speed. The use of the rotor blade angle
as a reference parameter is also proposed for a range which for
even higher wind speeds adjoins the full-load range, namely a
so-called storm range which for example can be between wind speeds
of 28 m/s and 42 m/s, to give just an example.
Thus ice accretion detection in the part-load range is effected by
way of the comparison of the detected power with a reference power.
In the full-load mode detection of ice accretion is effected by way
of the comparison of the set rotor blade angle with a reference
angle. Nonetheless it is preferably proposed that both criteria
always be checked in the part-load mode and/or in the full-load
mode, that is to say that the power is always compared to the
reference power and the set rotor blade angle is always compared to
the reference rotor blade angle. Ice accretion is to be assumed to
be occurring when at least one of those comparisons points to such
ice accretion. The underlying realization here is that the
respectively unsuitable comparison would not indicate ice
accretion, not even falsely.
Preferably slight adjustment of the rotor blade angle is already
effected in a transitional range from the part-load range to the
full-load range. By way of example the rotor blade angle can be
adjusted in the transitional range by an empirical value of
0.4.degree. per 100 kW. By virtue of the proposed simultaneous
checking both of the operating parameter power and also the
operating parameter rotor blade angle the described slight
adjustment of the rotor blade angle in the transitional range from
the part-load range to the full-load range does not cause any
problems as a result in regard to monitoring ice accretion. In
other words, this avoids the error of taking the wrong operating
parameter as the basis, if both are always monitored.
In a further embodiment it is proposed that a maximum value of the
operating parameter in question be used as the reference parameter
at least for sub-ranges of wind speed. That can also be provided
temporarily.
Preferably a wind speed-dependent reference parameter is used as
the reference characteristic. For each type of installation, such a
reference characteristic such as for example a wind speed-dependent
power characteristic can be stored at the factory as a standard
characteristic--also referred to as the default characteristic.
That standard reference characteristic is initially used directly
after the wind power installation is brought into operation.
Ultimately however each wind power installation has its own manner
of performance. That can be due to manufacturing fluctuations and
also in dependence on the respective erection site and further
circumstances. For that reason each wind power installation adapts
that standard characteristic in the course of operation thereof.
That is effected by using measured values under assumed normal
boundary conditions of the wind power installation, in particular
under conditions at which icing can be excluded. The measured
values are then processed to give a corresponding reference
characteristic. Known fluctuations which occur for example at
different ambient temperatures such as for example 3.degree. C. and
30.degree. C. in terms of air density can be taken into account by
a suitable adaptation factor. In that way it is possible to record
only one reference characteristic in spite of fluctuating boundary
conditions.
In a wind power installation, boundary conditions can occur leading
to a massive deviation in the installation-specific reference
characteristic relative to the stored standard reference
characteristic. Thus for example it is possible to provide wind
power installations with specifically targeted throttling of their
power output in order for example to limit the sound emission
caused by the wind power installation. That can lead to another
reference characteristic which the wind power installation records
in the course of operation thereof and which it uses as its basis
as an altered reference characteristic. As long as such adaptation
has not occurred or has occurred only for a part of the reference
characteristic, the reference characteristic is unsuitable for ice
detection. In that case it is proposed that the maximum value be
taken as the basis--in the present example the power limitation for
limiting sound emission. Ice accretion is then assumed to occur in
that case when the relevant value falls below that maximum value by
a predetermined amount, which can differ from the amount which
would be applied when using a reference characteristic.
Such a use of a maximum value can be effected portion-wise if parts
of the reference characteristic have already been adapted but other
parts have not yet, or such use can be effected time-wise or also
time-wise and portion-wise. For example it may also be considered
that the wind power installation is to be operated only at times
with a reduced power, if for example the operator of the network
into which the wind power installation feeds asks for a reduction
in the delivered power. In this case also the maximum value which
is given on the basis of the reduction is adopted as the reference
value. Just a short time later such a limitation can be removed
again.
In an embodiment it is proposed that, for heating the at least one
rotor blade, heated air is fed to the rotor blade and passed on a
flow path through the rotor blade to heat the rotor blade from the
interior. Rotor blades of modern and large wind power installations
frequently have hollow spaces which are separated from each other
by stabilizing connecting limbs. It is thus proposed that,
utilizing such hollow spaces, heated air is passed internally in
the rotor blade along the leading edge of the rotor blade into the
proximity of the rotor blade tip, that is to say the part of the
rotor blade that is remote from the rotor blade hub. There, in the
proximity of the rotor blade tip, there can be an opening in a
stabilization limb or other wall, through which the heated air
flows into a hollow space and back for example through a central
region of the rotor blade to the rotor blade root and thus
basically to the rotor blade hub. In that way it is also
advantageously possible to produce a circulating air flow by that
returning air being heated again and passed again along the leading
edge into the rotor blade. One or more fans and one or more heating
elements can be provided for that purpose.
Alternatively or additionally an electrical resistance heating
element such as for example a heating mat or a plurality thereof
can be arranged and in particular embedded at regions of the rotor
blade, that are to be heated.
A further embodiment proposes that a temperature is detected at or
in the proximity of the wind power installation, in particular an
outside temperature, and the wind power installation is shut down
if the detected temperature is below a predetermined minimum
temperature and if the detected operating parameter exceeds the
predetermined deviation relative to the reference parameter.
Optionally a fault signal is produced and/or outputted. For that
purpose, the underlying realization is that at temperatures below
0.degree. C. icing does not admittedly have to occur, but icing can
be excluded above a given temperature such as for example 2.degree.
C. The value of 2.degree. C. is slightly above the freezing point
of water and thus takes account of a slight tolerance in respect of
temperature measurement or slight local temperature fluctuations.
If therefore the criterion of ice accretion is detected by
comparison of the operating parameter with the reference parameter,
but the outside temperature which exceeds the predetermined
temperature value excludes ice accretion, it is assumed that the
situation involves a fault situation and it is advisable for the
installation to be at least stopped and preferably also shut down.
For detecting and evaluating the fault it is proposed that a fault
signal be generated for that purpose and communicated to a control
unit and/or passed to a central monitoring system by way of a
communication connection.
Preferably heating is effected when the temperature falls below a
predetermined temperature value such as for example a value of
2.degree. C. It is also possible to select for example a value of
1.degree. C. or 3.degree. C.
In a further preferred embodiment it is proposed that heating is
effected only when the detected operating parameter has exceeded
the predetermined deviation relative to the reference parameter for
a first predetermined minimum time. That therefore avoids heating
of the rotor blades being effected immediately upon a first
comparison between operating parameter and reference parameter,
that indicates ice accretion. Here on the one hand the situation is
based on the realization that the formation of an ice accretion
requires a certain time. In addition there is the possibility that
a slight ice accretion possibly deviates again on its own for a
short time or is reduced. Finally this also avoids a possible
individual defective measurement already triggering heating. The
first predetermined time can also be composed or modified, that is
to say for example there can be a minimum time of 10 minutes, in
which respect there does not have to be a requirement that ice
accretion was detected for an uninterrupted period of time of 10
minutes. Rather, it can be provided that this minimum time is
increased by times in which ice accretion was not detected in the
meantime. Advantageously such checking is effected by counters. By
way of example, a comparison between operating parameter and
reference parameter can be effected at a minutes rhythm--or at
other times. Each time that in that case a possible ice accretion
is detected, a corresponding counter is increased by a value until
it reaches a predetermined value of for example 10. If in the
meantime the situation occurs that ice accretion is not detected,
then the counter can also be counted down again.
Preferably an outside temperature is taken into consideration at
the same time so that generally ice accretion is assumed to be
occurring only when a predetermined outside temperature for example
in the range of 1.degree. to 3.degree., in particular 2.degree. C.,
is reached, or the temperature falls below that predetermined
outside temperature, and also times in which the outside
temperature is higher are generally not taken into consideration.
The above-described counter for detecting the minimum time
therefore counts up only when the outside temperature is
sufficiently low.
In addition or optionally it is also proposed that the wind power
installation is shut down only when the first operating parameter
was outside a or outside the second tolerance range for a
predetermined minimum time. That also avoids excessively sensitive
stoppage or shut-down.
It is desirable if, after a stoppage or shut-down, that is to say
generally after the wind power installation has been stopped, the
installation is re-started after a predetermined re-start time,
governed by detection of an operating parameter outside the second
tolerance range. That re-start time can be several hours such as
for example 6 hours. On the one hand, in the event of heating of
the rotor blades in the stopped condition after 6 hours it is
possible to reckon on successful de-icing, while on the other hand
that can be a sufficient time for any weather conditions to have
changed again. The wind power installation can now be started again
and can be at least partially run up, in which case criteria for
detecting ice accretion are also monitored in that process. If in
that respect criteria which point to ice accretion are found, the
operator should not wait too long to stop the installation again
and to again wait for the predetermined re-start period of time. It
is thus proposed that the wind power installation is stopped again
when the detected operating parameter lay outside the second
tolerance range for a third predetermined minimum time which is
shorter than the second predetermined minimum time. That third
predetermined minimum time can also be monitored by a counter. For
that purpose it is possible to use the same counter as for the
second predetermined minimum time. The shorter time is then
implemented by the counter not changing to zero after the stoppage,
but by it being reduced only by a few values. Accordingly the
counter is again, by a few values, at its maximum value which
results in a stoppage.
It is desirable if, in the case of heating, that is maintained for
a predetermined fourth minimum time. Here the underlying
realization is that heating is intended to effect thawing and/or
prevention of ice accretion. In that case the basic starting point
adopted is thermal time constants below which heating appears to be
less appropriate. Thus for example heating can be effected at least
for 10 minutes or at least for 20 minutes.
It is also proposed that, after termination of a heating operation,
renewed heating is effected only after a predetermined fifth
minimum time. That makes it possible to avoid rapidly switching the
necessary heating arrangement on and off. Presetting the
predetermined fifth minimum time can be effected for example by
using a counter which is preferably to be used for the first
predetermined minimum time. That counter can be reduced by a
corresponding number which corresponds to the fifth predetermined
minimum time and for heating purposes the counter would then first
have to be correspondingly counted up by those values.
In another embodiment the wind power installation has an
anemometer. The wind speed is measured by the anemometer and a wind
speed-dependent reference value can be obtained from a
corresponding reference characteristic or table. Preferably an
ultrasonic anemometer is used which does not itself have any moving
parts. Thus it is possible for the rotor blades to ice up whereas
the ultrasonic anemometer does not ice up or at least the icing
thereof is so slight that a wind speed can still be reliably
measured.
Preferably a wind power installation has a central control unit
with which a method of operating a wind power installation
according to the invention can be carried out. The control unit can
have implemented suitable program codes for that purpose for
controlling the installation and the control unit can also include
a data store which includes one or more reference characteristics
and/or tables with reference parameters which are used for
performing the method of operating the wind power installation.
It is desirable if the characteristic at least for a portion, in
particular in the part-load range, is stored in the form of a cubic
function, that is to say for the power in dependence on the rotary
speed or for the power P as a function in dependence on the wind
speed V.sub.W as follows:
P=a+b*V.sub.W+c*V.sub.W.sup.2+d*V.sub.W.sup.3
The coefficients a, b, c and d can be ascertained from measurement
values. A cubic curve also occurs when one or more of the
coefficients a, b and c assume the value zero if d is not equal to
zero.
Preferably there is also provided a heating device having at least
one blower and at least one heating element which can be integrated
in a unit. Preferably such a heating device is provided for each
rotor blade. It is also desirable if the rotor blade has a through
opening in the region of its rotor blade tip in the interior of the
rotor blade to divert an air flow for heating purposes in the
region of the rotor blade tip.
In another embodiment alternatively or additionally a resistance
heating element like a heating mat or an arrangement of a plurality
of heating mats is used.
In addition there is proposed a method of operating a wind power
installation having an aerodynamic rotor with at least one rotor
blade, which involves monitoring whether there is icing on the wind
power installation, in particular by an ice sensor for detecting
ice accretion, and in which the at least one rotor blade is heated
when ice accretion has been detected, in which case operation of
the wind power installation is continued.
Here ice accretion can be detected with a sensor or the ice
accretion is for example detected as described hereinbefore. With
this procedure it is also proposed that the installation is not
shut down in the case of an ice accretion, but continues to be
operated with heating of the rotor blades, in particular the
aerodynamic rotor of the wind power installation is to continue to
rotate and the wind power installation is to continue to feed
energy into the network.
In addition there is proposed a method of operating a wind park
comprising a plurality of intercommunicating wind power
installations, each having an aerodynamic rotor with at least one
rotor blade, which monitors whether there is icing at least one of
the wind power installations, in particular by an ice sensor for
detecting an ice accretion, and the at least one rotor blade of
each of the wind power installations is heated when ice accretion
has been detected, in which case operation of the wind power
installations of the wind park is continued.
Here the underlying realization is that precise and reliable
detection of ice accretion can require a special expensive sensor.
The environmental conditions, in particular weather conditions,
which lead to ice accretion, are however at least similar for the
individual wind power installations within a wind park. It may then
be sufficient to monitor only one wind power installation which is
representative of the wind park but at least a part thereof.
The communication of the wind power installations of a wind park
with each other is effected for example by way of an SCADA system
adapted to wind power installations (Supervisory Control and Data
Acquisition).
Even when using a sensor for detecting an icing condition it is
preferably proposed that one or more of the method steps or
features or criteria be adopted, which were described hereinbefore
in connection with the detection of icing by comparison of a
detected parameter with a reference parameter. That applies in
particular but not exclusively to the use of the delay times and
the use of counters. Evaluation of the outside temperature can also
be used in the same manner insofar as this can be applied.
Preferably heating is already effected when the outside temperature
is below a predetermined value such as for example in the range of
1.degree. C. to 3.degree. C., in particular 2.degree. C., without
further investigations of ice accretion being implemented. In that
case ice accretion detection is dispensed with and, below that
temperature value, continuous heating is effected until the
predetermined temperature is exceeded again. It was recognized here
that the additional energy generated by improving the aerodynamics
of the rotor blades by thawing the ice is greater than the energy
used for heating. The overall energy balance sheet can thus be
improved by the heating operation even when heating is always
effected at cold temperatures. It was realized that a greater
energy loss is to be expected if unrecognized ice accretion is not
combated, than if heating is effected unnecessarily. That applies
in particular when the heating power is controlled, as described
above, in dependence on the energy generated.
A possible way of implementing such temperature-dependent
continuous heating in terms of control technology provides setting
the above-described tolerance range to zero. In the example in FIG.
1 this means that P.sub.Heat is set to 100% of P.sub.Opt, or to an
even higher value.
In accordance with a further embodiment there is proposed a rotor
blade for fixing to a rotor blade hub, namely a hub of a rotor of a
wind power installation. The rotor blade includes a main portion
for fixing to the hub. The rotor blade further includes an end
portion for fixing to the main portion. In addition there can be
provided at least one intermediate portion and in that case the end
portion can be fixed to the intermediate portion, more specifically
in addition or alternatively.
The main portion and the end portion are initially provided as
separate parts in particular in manufacture and are assembled
later, in particular when erecting the wind power installation. The
assembly procedure is preferably implemented by screwing. In
particular in normal use the hub carries the main portion and the
main portion carries the end portion.
The main portion includes a blade root region for fixing to the hub
and a connecting region for fixing to the end portion and/or the or
an intermediate portion, wherein provided in the main portion is an
air guide tube for passing heated air through the main portion from
the root region to the end portion, wherein the air guide tube is
so designed that the heated air, on passing through, does not come
into contact with the main portion. Thus heated air is passed
through the main portion, which however is not used for heating the
main portion but is first intended to heat the end portion.
Preferably there is provided a rotor blade which is characterized
in that
provided in the main portion are regions having a flat heating
device for heating the rotor blade and regions having a thermal
insulation for preventing a heat loss from the rotor blade,
the main portion is made substantially from metal, in particular
steel,
the end portion is substantially made from a composite material, in
particular glass fiber-reinforced plastic (GRP), and/or
the end portion is partially insulated towards the exterior.
These features are preferably provided in combination but each in
itself also forms a desirable configuration. A combination of a
main portion of metal with an end portion of a composite material
makes it possible to use the advantages of a metallic material like
stability and protection against lightening, while at the same time
it is possible to provide a comparatively light rotor blade.
There is further proposed a wind park which has implemented a
method according to the invention.
FIG. 1 shows a graph illustrating the power of the wind power
installation, namely the power P generated by the generator, in
relation to wind speed V.sub.W. The characteristic identified by
P.sub.Opt represents a configuration for the power for the case of
power-optimal regulation of the wind power installation, as was
ascertained on the basis of a prolonged operating period of the
underlying wind power installation. The Figure also shows a minimum
power characteristic P.sub.min and a maximum power characteristic
P.sub.max. The two power characteristics P.sub.min and P.sub.max
enclose the power-optimized characteristic P.sub.opt at any event
in an initial region and form a second tolerance range Tol.sub.2.
If the detected power, with the wind speed V.sub.W measured in
relation thereto, deviates so greatly from the reference value
P.sub.opt that it is outside the second tolerance range Tol.sub.2,
that is to say below the characteristic P.sub.min or above the
characteristic P.sub.max, the wind power installation is stopped
and possibly shut down. For example in the range from the nominal
wind speed V.sub.N to the limit wind speed V.sub.G, as from which
the wind power installation is reduced in power, P.sub.min can be
75% of the power-optimized characteristic.
The maximum power P.sub.max is predetermined only for the part-load
range, namely approximately up to the nominal wind speed V.sub.N.
There is no need to further establish the pattern of P.sub.max
because in the course of the further variation therein, that is to
say from wind speeds of the nominal wind speed B.sub.N, greater
power levels than the respective value of P.sub.opt are not to be
expected.
In addition FIG. 1 shows a characteristic P.sub.Heat in broken
line. If the measured power value, in which case the power can be
averaged for example over a given time like 10 minutes, differs so
greatly at the wind speed in question from the power-optimized
value P.sub.opt namely it falls below it so greatly that the value
is below the characteristic P.sub.Heat but is above the
characteristic P.sub.min, operation of the wind power installation
is continued, the rotor continues to rotate, power is still
produced and the rotor blades of the wind power installation are
heated. No characteristic which is to be interpreted similarly to
P.sub.Heat is shown above the power-optimized characteristic
P.sub.opt. This means that, when the respective value of the
characteristic P.sub.opt is exceeded, heating of the rotor blades
does not occur in any case.
The broken-line characteristic P.sub.Heat thus forms a first
tolerance range Tol.sub.1 with the characteristic of P.sub.max. As
long as the detected power is in that first tolerance range, no
heating of the rotor blades is initiated, nor is the wind power
installation stopped. On the contrary, the wind power installation
continues to be operated unchanged. If however the detected value
of the power is outside the first tolerance range but within the
second tolerance range and thus between the broken-line
characteristic P.sub.Heat and the characteristic P.sub.min, then
the rotor blades are heated.
In the illustrated example, in particular in the full-load range,
the value of P.sub.Heat is approximately 90% of the value of
P.sub.opt. In the rest of the range the value of P.sub.Heat can
also assume for example 90% of P.sub.opt.
It is to be noted that the values for P.sub.Heat and also P.sub.min
are determined and illustrated for the entire relevant wind speed
range from V.sub.Activate to V.sub.A. Nonetheless, as from
approximately the nominal wind speed V.sub.N, monitoring based on
the comparison of a detected rotor blade angle with a wind
speed-dependently stored rotor blade angle becomes relevant, which
however is not shown in FIG. 1. Further monitoring of P.sub.Heat
and P.sub.min is continued, but basically such rotor
blade-dependent monitoring is not disturbance and in that range
should also not lead to detection of ice accretion.
FIG. 2 shows a sound-optimized mode of operation. In this
sound-optimized mode the power is not to exceed a reduced power
value P.sub.S to keep sound emissions within limits. The
installation-specific characteristic is intended to be
characterized by the characteristic P.sub.Sopt. In the case shown
in FIG. 2 however verification of the power characteristic for the
installation has not yet been concluded. The situation is therefore
based on a standard characteristic which does not take account of
that reduction and in relation to which an installation-specific
characteristic which takes account of that reduction could not yet
be completely detected. In the region of the limit wind speed and
also still before same therefore P.sub.Sopt still assumes the value
of the nominal power P.sub.N. In the illustrated example the wind
power installation was not yet operated or not yet operated
noticeably at wind speeds which are somewhat above the wind speeds
V.sub.H shown as an assistance aspect. Therefore P.sub.Sopt in part
still assumes the illustrated high values. As soon as the wind
power installation has been sufficiently often operated at the
remaining wind speeds approximately from the wind speed V.sub.H
which is illustrated as an assistance, the maximum value of the
optimized power characteristic P.sub.Sopt may involve the value of
P.sub.S which here is about 50% of the nominal power P.sub.N. The
power characteristic P.sub.Smin which is correspondingly calculated
as the lower limit is oriented to the configuration of P.sub.Sopt,
that in part is not yet correct. Thus, in the region between the
wind speed given as assistance and the limit wind speed V.sub.G the
configuration P.sub.Smin assumes the value of 75% of P.sub.Sopt.
When now--for the first time--the wind power installation is
operated with a wind speed in that range, a power level is set,
which does not exceed the value P.sub.S because that is the
absolute upper limit in the present case. For a wind speed V.sub.H
however such a power is also to be below P.sub.Smin. Consequently
the wind power installation would have to be stopped. To avoid such
unwanted stoppage a restricted minimum value is determined for
P.sub.Smin which is illustrated as the characteristic P.sub.SminB.
That characteristic is about 75% below the present characteristic
of P.sub.Sopt but at maximum up to 75% of the maximum permissible
value of P.sub.S. Thus stoppage of the wind power installation
occurs only when a power value below that characteristic
P.sub.SminB occurs.
It will also be seen from FIG. 2 that, for the wind speeds for
which the power value P.sub.Sopt does not exceed the maximum
permissible--sound-optimized--power P.sub.S, the configuration of
the characteristic P.sub.Smin and the characteristic P.sub.SminB
coincide. The configuration of the maximum power characteristic
P.sub.Smax is basically uninfluenced by the problems involved,
wherein the characteristic of P.sub.Smax ends upon attainment of
the maximum sound-optimized power P.sub.S.
FIGS. 1 and 2 show an installation having a nominal power of 2000
kW and a characteristic configuration sound-optimized to a power
value of 1000 kW shown in FIG. 2 as P.sub.Sopt.
The rotor blade 1 in FIG. 3 has a leading edge 2 and a trailing
edge 4. In addition the Figure shows a rotor blade root 6 with
which the rotor blade 1 is fixed to a rotor blade hub. Finally a
rotor blade tip 8 is shown, which is at the side remote from the
rotor blade root 6.
For heating the rotor blade 8 there is a heating device 10 arranged
in the region of the rotor blade root 6. Other configurations are
possible, in which the heating device 10 is arranged not in the
rotor blade but in the rotor blade hub in the immediate proximity
of the rotor blade root. Equally the heating device could be fixed
to the rotor blade hub, but in such a way that it projects into the
root region of the rotor blade root 6. Preferably the heating
device 10 is so arranged that an electrical connection between the
rotor blade 1 and the rotor hub is avoided.
The heating device 10 is only shown here in the form of a symbol,
having a blower and at least one heating element, in particular a
resistance heating element like for example heating wires. The
heating device 10 then blows heated, at least warmed air, along a
first chamber 12 arranged directly adjacent to the leading edge 2.
Here the hot air produced is symbolically indicated by arrows as an
air flow 14. The hot air flow 14 then flows to the proximity of the
rotor blade tip 8 and there passes through an opening 16 in a wall
18. In that way the air passes into a central chamber 20 and flows
therein as a return flow 22 symbolically indicated by corresponding
arrows, back to the rotor blade root 6. The air which flows back
with the return flow 22 is drawn in again by the heating device 10
in the region of the rotor blade root 6, heated and blown into the
first chamber 12 again.
Heating is thus effected substantially by a circulating air flow.
It is to be noted that the rotor blade 1 is only diagrammatically
illustrated to explain the functionality of the heating process. In
particular the first chamber 12 and the central chamber 20 are
shown in highly simplified form here.
Ice accretion detection by monitoring the installation power which
forms the basis for the present method of operating a wind power
installation is based on the aerodynamic properties of a rotor
blade being altered by icing. To be able to measure and monitor
those installation-specific aerodynamic properties it is necessary
or at least desirable to record them when the installation is
running unlimitedly, that is to say in particular is not limited in
terms of its power in order then to compare those properties or
corresponding values with the data which are measured at
temperatures around or below the freezing point.
When the installation is first brought into operation, the basis
adopted is a standard power characteristic which is typical for the
rotor blade of the respective installation, and that is stored in
the control unit 11 of the wind power installation. That
characteristic is a measured power characteristic in relation to
the wind speed for the respective type of installation or
blade.
At outside temperatures of higher than +2.degree. C. that so-called
default characteristic is progressively corrected in dependence on
the measured wind speed. For that purpose a respective average
value of the wind speed and of the power are typically formed over
60 s. To compensate for fluctuations in density which are caused by
different air temperatures the measured power is respectively
provided with an outside temperature-dependent correction. In that
way scarcely any part is played by whether the characteristic is
recorded at +3.degree. C. or +30.degree. C. The value of the power
characteristic, that belongs to the measured wind speed, is then
corrected upwardly or downwardly in dependence on the measured
power by a small part of the deviation, from the stored value. In
that way, depending on how long the installation was operated at
various wind speeds, an installation-specific power characteristic
is formed in relation to the measured wind speed.
Correction of the characteristic is effected in one case only when
the installation is running unlimitedly. That means that neither
are the rotor blades moved back beyond the predetermined minimum
blade angle, that is to say reverse-pitched, nor is the
installation power limited by a maximum power which is below the
set nominal power. In addition, as already mentioned above,
correction of the characteristic is effected only at outside
temperatures of higher than +2.degree. C., as below that
temperature there is the risk of ice accretion, which would then
lead to a falsification of the characteristic and would make ice
accretion detection ineffective.
As the installations are operated in the power-optimized and
sound-optimized mode of operation with different parameters it is
necessary to record independent characteristics for the two
operating states. The contents of the stored power characteristics
for the power-optimized and sound-optimized modes can be manually
displayed and/or selected.
The power characteristics are recorded in operation of the wind
power installation, in which respect recording is stopped at
temperatures of less than or equal to +2.degree. C., and a start is
made with ice accretion detection. A counter is used for that
purpose, which counts up at outside temperatures below 2.degree. C.
and correspondingly permanently stores the possibility of
installation icing. At outside temperatures<+2.degree. C. the
timer for ice accretion is counted up within one minute to
360.degree. C. When it reached that value the control unit
recognizes that icing is possible and a corresponding ice accretion
detection method is activated. It is only if the outside
temperature is higher than 2.degree. C. that the counter begins to
count slowly again towards zero. In that respect that counting-down
speed depends on the outside temperature. The higher the outside
temperature is, the correspondingly faster the timer is counted
down to zero again and ice accretion detection is concluded and the
recording of the characteristics is continued.
If icing is basically possible because of low temperatures the
control unit begins to compare the currently measured average power
to the stored characteristic. For that purpose a maximum and a
minimum power in relation to the respectively measured average wind
speed is determined on the basis of the set parameters for
monitoring of the power characteristic.
By way of example a tolerance band is determined around the
recorded characteristic, the width of which can be different. For
example the basis can be a width for the tolerance range up to a
wind speed of 10.5 m/s. In that respect a tolerance value can be
used, which gives the spacing between the recorded characteristic
and a lower or upper limit. A power window, in which the power of
the installation can range, is calculated on the basis of that
value by the stored power characteristic. The lower value of the
power window is the power value of the stored characteristic, at
the measured wind speed, less said tolerance value. The upper value
is the value of the power characteristic, that belongs to the
measured wind speed plus said tolerance value.
The tolerance value can be specified for example as a relative
value of the power characteristic and can be for example 75% of the
power value in question of the power characteristic. In other words
the tolerance is 25% below or above the characteristic.
As soon as icing of the rotor blades is assumed to be occurring and
the power P which is typically averaged over 60 seconds--which can
also be referred to as the current power P.sub.Akt--falls below a
lower limit value P.sub.min, a corresponding counter is increased
by the value 1. The installation stops with a status `ice accretion
detection: rotor (power measurement)` as soon as the counter
reaches the value 30.
The installation automatically resumes operation when the outside
temperature has risen for a sufficiently long time to a value of
more than 2.degree. C. and a timer for detection of ice accretion
has correspondingly counted down again to zero. In a similar manner
it restores operation automatically after blade de-icing is
terminated. Even if icing is still possible the installation then
undertakes an attempt at starting for example at a spacing of 6
hours in order to check whether the rotor blades have become
ice-free again. For that purpose the above-mentioned counter is set
back from 30 to 27. As soon as the installation is started the
power is monitored again. If the blades are still iced up, that
should result in the counter counting up again and the installation
being already stopped after three counter operations, in the
present example therefore after three minutes. If the blades are no
longer iced up or are only still slightly iced up, the counter
counts down and the installation remains operating. That function
provides that the stoppage times due to ice accretion can be
shortened.
In an embodiment of a wind power installation there is provided a
circulating air blade heating system. The circulating air blade
heating system comprises a heating blower of a power of 20 kW per
blade--in another configuration this is 25 kW per blade--which is
mounted in the blade and which drives air heated up to 72.degree.
C. along the leading edge of the blade to the blade tip. In that
way it is possible both to de-ice the rotor blades when the
installation is stationary and also to keep the rotor blades
ice-free when the installation is operating in most cases. The
present method therefore concerns both a method in which an ice
accretion can be detected and eliminated and also a method which
can be used substantially preventatively in order to prevent ice
accretion or at least preclude same.
Besides a circulating air blade heating system, in accordance with
another embodiment there is proposed a cloth heating arrangement
which falls within the generic term of an electrical resistance
heating element or an electrical resistance heating arrangement. In
that case a wire mesh laminated into the blade is heated with a
high current by way of an isolating transformer. Such heating
arrangements operate in particular with power levels of between 8
kW and 15 kW per blade. The described mode of operation of the wind
power installation can basically use both kinds of blade heating
arrangement.
In principle manual de-icing can also be effected with such a blade
heating arrangement. If however operation of the blade heating
arrangement is in an automatic mode the blade heating arrangement
switches on as soon as a counter of an ice accretion detection
system has reached a corresponding value, under the above-described
criteria. Typically such a counter first reaches a value which
corresponds to at least 10 minutes. For example the blade heating
arrangement then remains in operation for at least 20 minutes. In
that way ice which has already formed on the rotor blades is
thawed. The efficiency of the rotor is improved and the ice
accretion detection counters go towards zero again if de-icing was
at least partly successful. In that way, with a minimum switch-on
period for the heating arrangement, this prevents the installation
having to be stopped because of ice accretion.
Presetting of the maximum reference power of the blade heating
arrangement is possible. In an embodiment that value can be set at
between 0 kW and 85 kW. The maximum value of 85 kW is composed of
about 3.times.25 kW for the three heating registers and 3.times.3.3
kW for the three fans.
Then, having regard to the currently prevailing installation power,
the blade heating system takes no more than said set reference
power on the five-minute average. If for example a value of 40 kW
is set for the reference power then the blade heating arrangement,
with the installation stationary or at 0 kW installation power,
operates with a maximum of 40 kW, namely 10 kW for the fan and
3.times.10 kW for the heating system. If operation of the blade
heating system is switched on with the installation running the
blade heating system is then also operated with increasing
installation power at a higher power level and from 30 kW
installation power--this for example can be 45 kW in the case of
another installation--reaches the maximum power of 70 kW, which can
be for example 85 kW in another installation.
The minimum heating period of the blade heating arrangement can be
selected to be for example between an hour and ten hours. The
heating period depends primarily on the set reference power and the
outside temperature. In addition wind speed and the degree of icing
play a part. Empirical values have shown that a heating period of
between three hours and four hours can be sufficient in most
cases.
FIGS. 4 and 5 show an embodiment of a multi-part rotor blade. The
rotor blade 400 has a main portion 402 and an end portion 404. The
main portion 402 has a connecting region 406 and a blade root
region 408. The main portion is connected to the end portion 404 in
the connecting region 406. There is also a trailing edge segment
410 fixed to the main portion.
An air guide tube 412 is arranged as an air guide in the main
portion. The air guide tube 412 is coupled to a heating blower 414
for producing and delivering heated air. The heating blower can be
in the form of a blower with a heating radiator. The heating blower
414 is disposed in the blade root region 408 of the main portion
402 and there produces the heated air and blows it into the air
guide tube 412. In another embodiment, the heat for the heating
blower 414 comes from the generator in the pod, which naturally
produces heat when it makes electricity. The air guide tube 412
guides the heated air through the main portion 402 to the
connecting region 406 where it passes into the end portion 404 to
heat it. The heated air is thus guided through the air guide tube
412 without in that case issuing into the main portion 402. The
heated air guided in the air guide tube 412 is thus not used for
heating the main portion 402. Instead of the air guide tube 412 it
is also possible for example to use a hose or other suitable
structure with which the heated air is guided through the main
portion. The air guide tube can have an insulation to minimize
unwanted heat dissipation of the heated air.
Provided in the end portion 406 are air guide plates 414 which
guide the heated air through the interior of the end portion in
such a way that the end portion is heated thereby. Preferably
support plates in the rotor blade are used as the plates. The
plates guide the heated air on a feed path identified by the arrow
416 to a rotor blade tip 418. Shortly before the rotor blade tip
418 the air is reversed in direction and flows back on a return
path identified by the arrow 420 to the connecting region 406.
De-icing in particular is to be effected by the heating action.
Thermal insulation can be provided in the end portion 406 in the
region in which the air flows back, as indicated by the arrow 420,
to avoid heat losses there.
From the connecting region 406 the air flows through the main
portion 402 back to the root region 408 in which the heating blower
416 is disposed. In this case the air flows through the internal
space in the main portion on a return path identified by the arrow
422, in contrast to the feed path, without using an air guide
tube.
Alternatively it is also possible to provide for that return path
an air guide tube which can have an additional insulation to avoid
heat dissipation and thus heat loss.
The heating blower 414 is arranged in the blade root region 408
which has a fixing flange 424 for fixing to a rotor blade hub. In
that way the heating blower 414 is disposed in the region of the
rotor blade hub and is accordingly readily accessible for
maintenance operations. Thus heated air for heating the end portion
404 can be easily fed from a position in the proximity of the rotor
hub. Preferably, as in the case of the illustrated rotor blade 400,
the main portion 402 is made from metal such as for example steel,
thereby providing lightening protection for the heating blower
because the main portion acts as a Faraday cage in which the
heating blower is arranged. As in the illustrated embodiment the
end portion can be made from glass fiber composite material
(GRP).
Heating mats 426 are provided for heating the main portion.
* * * * *